Multi-deck filters are pressure filters in which the filter-plate frames rest against one another and are pressed together. The filtrate that is fed to the filter plate frames is discharged through the frames and its outlet openings. The filtering process takes place with the plates pressed together, so that a filter belt is positioned between two adjacent filter plates which are clamped in place. The filtrate flows through the filter plates, while particles of dirt are collected by the filter belt. The dirt cake which is collected must be removed from the multi-deck filter from time to time. For this purpose, the filter plates, together with their frames, are unclamped and separated by a suitable device so that the dirty portion of the filter belt can be moved out from between the filter plates by means of a transport device and replaced by a clean portion of the filter belt. The filter plates and frames are then clamped together so that the multi-deck filter is again ready for filtering.
In conventional belt filters, the filter cake is removed by a deflection roll of the filter belt. The filter cake is broken up by the deflection of the filter belt and formed into pieces which then drop into a receiving means below the filter belt. In multi-deck filters where several chambers are positioned one above the other and thus several filter belts also travel one above the other, this method of removing the dirt filter cake is disadvantageous. Because the filter belt must be deflected, the subsequent winding of the filter belt from which the dirt filter cake has been removed cake onto collecting rolls is impeded due to considerations of space. Problems also arise with regard to the guiding of the belt.
European Patent No. 03 04 579 discloses a device in which the filter belt is guided around a deflection edge positioned obliquely to the direction of the belt and turning the bottom face of the belt upward. In this way, better guidance of the belt is obtained while effective detachment of the filter cake is also achieved. This device, however, is very expensive due to its large number of deflection rolls and is thus subject to disturbance, and furthermore requires extensive maintenance.